1. Field of the Invention
The invention relates to a charge accumulating system and a charge accumulating method of a nonaqueous electrolyte battery.
2. Description of the Related Art
Nonaqueous electrolyte batteries for charging and discharging due to lithium ions moving between a negative electrode and a positive electrode have been intensively researched and developed as high energy density batteries. Recently, such nonaqueous electrolyte batteries are being demanded to be improved in high temperature properties such as stability, cycle characteristic, and storage performance in a high temperature environment, aside from enhancement of the energy density required so far.
At the present, a nonaqueous electrolyte used in a nonaqueous electrolyte battery is generally a nonaqueous electrolyte of an organic solvent system obtained by dissolving an electrolyte in an organic solvent. Since the organic solvent is combustible and volatile, various safety devices are provided from the viewpoint of enhancement of safety, which are factors for lowering the volume energy density.
It has been proposed to improve the high temperature characteristics of a nonaqueous electrolyte by using an ionic liquid which is noncombustible and nonvolatile without using the organic solvent. The ionic liquid is a kind of salt composed of cations and anions and exists in a liquid state at room temperature. The ionic liquid is strong in ion bonding property, and is hence nonvolatile and noncombustible.
JP-A 2004-015876 (KOKAI) discloses a nonaqueous electrolyte battery of an organic solvent system, in which the cycle performances are improved by setting low a charge voltage along with elevation of temperature.